1. Field
Methods and Apparatuses consistent with exemplary embodiments relate to a method and apparatus for correcting an image, and more particularly, to a method and apparatus for improving image quality by removing noise such as a false contour or a halo that may occur during a process of transmitting or processing an image.
2. Description of the Related Art
When an image is displayed on a display included in various media reproducing devices such as televisions, portable media players, smart phones, Blue-ray disc players, etc., if an input image of the display has a number of bits smaller than that of an output image, false contour noise may occur. In particular, the false contour noise may easily occur in an image including a region in which pixel values vary smoothly. Thus, there is a need for a technology for naturally expressing the region in which the pixel values vary smoothly by preventing or removing the false contour noise.
In the related art, whether there is a gradual increase or a gradual decrease in pixel values of neighboring pixels of a pixel of interest is determined, and, based on a change amount between a pixel value of the pixel of interest and the pixel values of the neighboring pixels, a region having a change amount greater than a threshold value is determined as a region including the false contour.
In more detail, the related art technology measures the change amount between the pixel value of the pixel of interest and the pixel values of the neighboring pixels, and, when there is a gradual increase or a gradual decrease in the measured change amount, determines that the pixel of interest is included in a flat region. When the change amount of the pixel values of the neighboring pixels gradually increases with a temporary decrease or gradually decreases with a temporary increase in a region of interest, the false contour is determined to be present in the region of interest.
However, a false contour detection method of the related art has a low accuracy in detecting a false contour in a general broadcast image which includes a large amount of noise. Also, a false contour detection method of the related art has a substantially low accuracy in detecting the false contour from a low gradation image having generally low pixel brightness or from an image including a low gradation region. Thus, since the related art cannot accurately detect the false contour, it is difficult to improve image quality by entirely removing the false contour.
On the other hand, contrast enhancement (CE) is an image processing method of changing values of pixels to increase contrast between the pixels included in an input image by applying, to the pixels, a function of converting colors, intensity, or brightness of the pixels included in the input image. For example, a method of performing enhancement processing on the image may include global CE and local CE.
The global CE involves applying a conversion function to an entire image. The local CE involves respectively applying different conversion functions to a plurality of regions included in the image. The local CE may have an advantage of further enhancing contrast between regions compared to the global CE. However, the local CE may cause deterioration of image quality through, for example, a halo or false contour.
The deterioration of the image quality caused by the local CE is described by way of an example in which an input image includes a wide flat region and an edge with strong intensity, and pixels of the flat region of the input image have substantially the same pixel values. Even when the pixels of the flat region of the input image have substantially the same pixel values, when the local CE is performed on the input image, different conversion functions are applied to regions of the input image. That is, different conversion functions are applied to a region adjacent to an edge and regions distanced away from the edge in the flat region.
Therefore, pixels included in the flat region adjacent to the edge and the pixels included in the flat region distanced away from the edge may have different values. That is, when the local CE is performed on the input image, the deterioration of the image quality due to, for example, a halo or false contour may occur in the flat region. Thus, a technology for preventing image quality from being deteriorated while maintaining an effect of increasing definition of an image using the local CE is needed.